The Mariners also received outfield prospect Johermyn Chavez, a 20-year-old who hit 21 home runs in low Class A ball in 2009.
"The thought process behind this, from our estimation, is the fact that we were a little uncomfortable with the current status of our bullpen," said Mariners general manager Jack Zduriencik, who mentioned some uncertainty with how right-hander Sean White will rebound from a shoulder injury that ended his 2009 season in early September.
"Last year, [the bullpen] was a big part of our success. When you look at a kid like Brandon League, who's a power arm with a great sinker and a swing-and-miss fastball, that gives you an additional arm that's experienced and will fit into our ballpark very nicely as well as on our pitching staff."
Chavez, a native of Venezuela who will turn 21 on Jan. 26, projects as a big league power prospect at 6-foot-3 and 220 pounds. Chavez hit .283 with 21 home runs, 89 RBIs, and a .346/.474/.821 on-base-plus-slugging line while playing for low Class A Lansing in 2009.
"You're never really sure about players that you get in A ball, but he is 20 years old, and when you look at a guy who hit 21 home runs in the Midwest League, there's a degree of impressiveness here," Zduriencik said.
In League, the Mariners get another hard-throwing right-hander to enter into the late-innings mix in Spring Training alongside last year's setup man, Mark Lowe, and closer, David Aardsma.
League, 26, set a career high with 67 appearances in 2009 and struck out 76 batters in 74 2/3 innings. In his career with Toronto, League went 7-10 with a 4.09 ERA in 202 1/3 innings. He can hit up to 97 mph on the radar gun, and he's already familiar with Seattle pitching coach Rick Adair from when the two worked together at Double-A New Hampshire in 2004.
"It's definitely exciting whenever you see a team make a lot of moves and that they have just one goal in mind, and that's to win," League said. "I'm flattered that they considered me in their moves and made me a part of their organization.
"And I have a lot of great memories about Rick. He taught me a lot. He's worked with John Smoltz in the past. He's not trying to compare me to Smoltz, but he helped me out a lot with mechanics and the mindset of being a late-inning guy and all that good stuff."
Zduriencik said Mariners scouts, particularly former Toronto advance scout Todd Greene, not to mention Adair, raved about League, and that the trade was the product of "at least 15 phone calls" with new Blue Jays GM Alex Anthopoulos, convrsations that began over a month before the early December Winter Meetings in Indianapolis.
"As we walked through this, it was difficult to give up a very talented young pitcher like a Brandon Morrow," Zduriencik said. "We do feel that Brandon is going to be a very successful big league pitcher.
"It was not an easy decision. We debated this thing for over a month. ... At the end of the day, he fit their need very well, and Brandon League right now fits our need."
Anthopoulos said the Jays feel League is about to "turn a corner" in 2010 and praised Chavez's work ethic, calling the trade "a reflection of how much we like Brandon Morrow.
"We had to give up two really good players," Anthopoulos said. "I think from both Seattle's perspective and our perspective, this was a good baseball trade for both teams. It solidified their bullpen and it gives us an opportunity to have a high-upside starter."
Meanwhile, the Mariners are saying goodbye to another first-round pick from former general manager Bill Bavasi's tenure. Zduriencik also has dealt 2005 first-rounder Jeff Clement, who was traded to Pittsburgh in July, and 2007 draftee Phillippe Aumont, who was sent to Philadelphia as part of the recent four-team deal that brought Cliff Lee to the Mariners and Roy Halladay to the Phillies.
Morrow, 25, was taken No. 5 overall in the 2006 First-Year Player Draft and shuttled between starting and relieving in several bigleague stints.
Last year, he opened the year as the team's closer, lost the job early in the season, and was eventually groomed in Triple-A to permanently be a starter. Morrow resurfaced in Seattle as part of the starting rotation and clicked in his last outing of 2009 when he threw eight one-hit innings against the Oakland A's. Morrow was unavailable to comment Wednesday.
"Now that we all look back on it, it may not have been the best thing in the world for Brandon," Zduriencik said, referring to switching back and forth from relieving to starting and Triple-A to the Majors.
"... I think in Brandon's case, he will benefit from everything he's been through, and at the end of the day he'll come out and be a better pitcher for it."
Morrow was 2-4 with a 4.39 ERA in 69 2/3 innings for the Mariners in 2009 and 5-3 with a 3.60 ERA over 10 starts with Triple-A Tacoma. Overall, Morrow has gone 8-12 with a 3.96 ERA in 197 2/3 innings with Seattle. In 15 career starts, he has gone 4-3 with a 4.42 ERA.
He had been projected to be a part of the Mariners' 2010 starting rotation, but now Zduriencik could be pounding the pavement for a fifth starter.
Another trade could be in the works, and the free-agent market remains an option, too, especially considering that former Mariner lefty Jarrod Washburn, Ben Sheets, Chien-Ming Wang, Smoltz and other quality names are still available.
For the ever-active Mariners, still swinging deals two days before Christmas, nothing would be surprising.
"Our ears are open and we're always looking for ways to get better," Zduriencik said. "We'll continue to explore our opportunities and options. There are names out there, certainly names that intrigue you, certainly names you have interest in.
"Who knows what will happen as we move forward?"