I've had numerous cops drive by me when I was hitching in Canada, I just smile and wave, usually they wave back (although I have kept my thumb out when I couldn't spot the sirens at night). I had one park behind a bush and stake out me and my comrade ( i assume to nail an unsuspecting kind driver) so we just turned our backs and ate lunch until he drove off. in ottawa we got rides into town from a cop (which we needed and also told to stay off the split highways from a different cop). Other then that in Canada I've never had a problem. I spend most of my time in BC and it seems like no cops on the highways there give two shits about it. Or at least don't give two shits about ME hitching, everyone has different stories of course.