Acquiring Burns, at the cost of Marner or Nylander, makes little sense for Toronto.
Imagine a hypothetical world where Toronto didn't have Reilly. In that case, they should trade Nylander + extras to get Burns. That makes sense...sure Burns is much older, but Toronto's windows is open NOW and they need a superstar defenseman more than they need another really good young forward player. I would imagine that given the age of the roster, the window would be open for a long time, but why wait? Defensemen like Burns are rarely available. I would even say a trade involving Marner for Burns is something Toronto should consider.
But, Toronto has Reilly. They have player, who, I think, is already an elite D-man or very close to it.