If you live in southern Ontario, visiting America is easy. Short drive, cross a bridge, off you go.
My work visits to America were to places slightly less scenic. In no particular date order: to Washington for an international conference on Ozonation; to Pittsburgh for a water treatment plants and distribution system automation study/design project; to Cleveland for a water pumping station upgrade of instrumentation and controls pre-design study; and to Erie, PA to present a conference paper about Heavy Metals Removal using Lanthanum Oxides (what a barn-barner); and a small plane fly-in to some field (literally) to inspect polymer process equipment at a wastewater treatment plant. This latter trip was probably the nastiest encounter with US Customs: landing at Detroit Municipal airport (with walk-off access to America) needed a call to ground control before landing requesting that customs officials meet the plane. After an hour wait outside on a very hot day, customs officials (one ludicrously overweight and his rookie sidekick who was going to be shown how to deal with furriners) showed up.
But the all-time favourites were regular visits to a Buffalo-area wastewater treatment plant to work on automation designs for stormwater modulation.