

TOR break up one of their massive risky contracts; DAL clear out some of their forward logjam and add facilitators and 2nds; POR clear out some of their point guard logjam, add starting PF
FULL DISCLOSURE: Am a Mavs fan.
I think this trade helps all three teams in different ways.
Raptors have a several big, expensive deals for guys that were overpaid and Quickley is one of those deals. Last year he had a bounce-back year, but that's after two years of missing a lot of time. He still has 3 years at 32.5M remaining and isn't a star. Here they break up that salary. They would need a PG if they traded him, so in this trade they get back a young PG with upside in Scoot who will be lost in Portland's PG-heavy rotation. They were also 21st in the league in 3P% last year and adding an all-time great helps them shore that up.
The Mavs probably need at least one more PG as Kyrie is coming off a major injury and Sergio De Larrea is a rookie. Quickley is an immediate upgrade that gives them insurance if Kyrie needs more rest on B2Bs or gets re-injured. He's expensive but the Mavs don't really have any bad contracts right now and have a huge glut at wing/forward where they don't have minutes to develop their young guys because vets like Klay and Washington deserve bigger roles. For taking on an expensive salary and giving up two solid vets the Mavs get 2 2nds to help replenish their diminished draft stock. Quickley is too good to give up a 1st to dump but a 2nd may be reasonable.
Portland turns their glut of PGs into a starting PF and replace the loss of Grant.
Krejci can go to either Dallas (Pic 1) or Toronto (Pic 2) and this trade succeeds. Another PG in Portland's glut of PGs, but a tall one. If Dallas takes him, they will need to cut someone regardless to pare down their roster to 15 by end of preseason (this site doesn't show Moussa Cisse being re-signed). Same is true with Toronto. Toronto may want him as insurance in case Scoot doesn't pan out. I'm fine with it either way.