From Toronto - Kapanen + 3rd round pick for Colorado's 1st round pick. (16th overall)
Let's be honest here, these teams don't fit very well for a trade. Leafs real need is a RHD, and Colorado isn't giving that up. Leafs secondary need might be prospect C's... but then, Colorado doesn't really have much there either that they can give away.
Casually, Colorado could use some secondary scoring, and another RW. I'm just going by stats here, and after Rantanen, the next RW in scoring is Sven... maybe someone is playing off their regular position, but I'm unaware if that's the case, so apologies. Kapanen is worth 1st round in the high twenties, but not 16 OA, so adding a third to even it out.
Leafs would probably target RHD Seider with the pick. Which long-term fills a need, but not right now...
I'm not sure if it's an ideal trade for either team, but it's about as good as I could find.