no problem

no problem if following conditions are meet.
1) go by bufflo, NY.
2)at night by rental car, after 10:00pm
3)when they ask you how long you left canada, tell me like two months. you can tell them you go to toronto to visit friend. no problem.
Maybe they will ask you I-94 but do not scare, they know a little about I-94.

I have been to Canada 4 time since last year Oct.
1st) did not ask me at all.
2nd) asked me how long I am out of canada, I told him two months and he let me pass.
3rd) asked me if the car it belongs to me. I told her it is rental car and show her the rental agreement. she let me in.
fourth) ask me the I-94 card and I gave her copy of my H1b approvel and she is cool.

So do not worry, no problem. those from my personal experience.