Definitely a different world today with international roaming on our cell phones, but I have traveled to Canada several times and just got back from the Bahamas yesterday. I have not had a horrible experience yet. Night before last, I called customs and told them that I planned to arrive at about 11:45 the following day from Freeport. (Note, customs would not have been open if I tried to call only an hour or two out, in reference to the OP) I didn't quite hit it on the head, but we touched down a few mins before noon I think. Taxied to the ramp, told the line guy I needed fuel, customs cleared us, line guy towed us over and fueled us up (we were #3 or 4 in line) and we were back out in the air in under 45 mins.
Coming back from Toronto (for a $100 hamburger) was my worst experience, in that, I called CBP at Buffalo and told them I planned to leave in an hour. They told me they needed 2 hours advance notice (regs say 1). So I asked if I could go to a different POE (Binghamton) and he was like, "That's fine." I said, "OK, have a good day," and he cut me off. I thought he was going to continue to be snippy, but instead, he said, "I can give you their phone number real quick." So he went from snippy to helpful REALLY quickly! If that's the worst experience I have, awesome.
Mind you, my wife is Canadian, so we always look like we have a reason to be there (she wasn't with me for the Toronto $100 hamburger), so that helps. Besides, between being married to an immigrant, traveling internationally at least once/year, and working for a federal law enforcement agency...if there's something the government doesn't know about me, I probably don't know it either!