It's not true.
The Raptors can't take on any salary without significantly lowering their offer to Hedo Turkoglu. That $2mil of Stack's contract counts on their cap. Nothing to this rumour.
True, but all Toronto would have to do is trade Kris Humphries to a team with cap space (Memphis, OKC, etc).
They could also send out min-level contracts for draft picks, and/or cut Quincy Douby, whose contract is not guaranteed.
So they give up Kris Humphries and get what from Dallas to make it worth their while?
Also, does Memphis has cap space anymore after taking on Randolph?
How badly does Cuban want Marion in Dallas? That's the question. Toronto won't want additional payroll back, so we're probably looking at future draft pick(s).
EDIT: looks like Dallas owes NJ its own 2010 1st rounder, and owes Indiana a 2nd rounder in 2010 or 2011. Dallas does own a 2nd rounder from Portland in 2010 (either Portland's own, or one via Chicago, whichever is worse). So any draft picks sent to Toronto would be paid well down the line.
Memphis should still have plenty of cap room to absorb Humphries' deal.