Evidently, he's about to become a very rich Canadian.
(Alternative PI link, which says the deal's worth about $50m/5yr instead.)
As the news washes over me, I'm prepared to let the rationalization stage begin - Burnett's got an extensive medical history, suboptimal mechanics, and a questional performance record for a supposed "ace." Guaranteeing him five years is one hell of a risk.
However, he is/was the best pitcher available this offseason, and his imminent decision to sign with Toronto (or St. Louis, but whatever, the point's still valid) means that the Mariners really have to rachet up their pursuit of Kevin Millwood, or else miss out on a good opportunity to land a solid #1/2. The rest of the free agent starters just aren't that appealing, and I don't see any other Josh Becketts being made available on the trade front (unless you feel like getting the short end of the stick in a Zito deal). Kris Benson? Carl Pavano? Meh. They don't really do it for me.
Maybe it's just as well - Millwood's the safer bet going forward than Burnett (albeit with a lower ceiling), and if I had to give a big contract to any free agent pitcher this winter, it'd probably be him. Still, though, I'd be lying if I said I wasn't just a little disappointed.