I've never seen a US immigration/customs priority line anywhere. I don't think they allow that. The only one is Nexus, and you don't need to be elite for that.

There is a priority security lane. However, aside from the post-christmas, check everyone's bag security, I've never seen a need for it. Usually, any customs line pretty much acts as crowd control for security, so there's usually no more than 3 or 4 people ahead in any of the security lines.

Whoops. thought you meant YYZ somehow, but read YUL now. Not sure what the security line is normally like there, but there certainly is a priority one.