Oh, wow, I've been looking for a proper veal sandwich in this area for years! Sadly, I've only come across good, but nothing great. I've had one at the Longo's on Hwy 7 and Woodbine, which has been pretty good at times. I can't say I've had much success with Nino since they moved. And Dante's makes a fantastic sandwich, but it's far from what you'd expect a traditional sandwich to be. There used to be a spot on Yonge just north of 16th, a purely italian sandwich place, and that was quite good... but it's gone now.
I haven't seen veal sandwiches at Weston Foods for a while. I like Old Mill bakery (Oxford Street, just west of Yonge, one light south of Elgin Mills); it's from a steam table, but it's not bad.
The much-maligned Dante's makes a huge veal sandwich. It's pricey, but I usually get two meals out of it. However, there's so much loaded on it that you don't get much veal taste.
Nino D'Aversa (Yonge & Glen Cameron) has a Veal Sandwich that has a following. I like it, but I like others (discussed in another thread) better.
On market days (Thursday-Saturday), there is a place in the York Farmer's Market that serves a veal sandwich, which is passable.
Some days, Longos (Bayview & Laureleaf) will have veal cutlets at their hot counter, but not everyday.
I'll throw out the names of a few other places that might have it, and let others confirm or deny: Wimpy's, Steve's, Il Fornelo and Weston Foods (Yonge south of Major Mac).
I find it worth the trip to Panini in Woodbridge, Weston & 7.