PaddleTime, as one who has paddled for 72 years, owned 21 different canoes and kayaks, and who has paddled lots of other canoes, let me try to simplify things for you:
Get a Souris River Quetico 18.5.
Why? Because if you are committed to the durability of epoxy construction for whatever reason, there aren't many epoxy-built, three-person canoes on the market. Swift and H20 will make them only for an expensive up-charge, and it's not clear that their 18+ foot models have the stability, capacity or durability of a Souris River Quetico 18.5.
Generally, for seaworthiness in waves, you don't want significant tumblehome in a big tandem canoe, and modern composite models won't have much, if any. Tandem paddlers sit in the ends of the canoe, which are narrow places that don't need tumblehome for vertical paddle placement, and the ends are usually flared or cheeked a bit to deflect waves. In modern times, shouldered tumblehome in the center of a canoe was initially developed so that a centrally-seated solo paddler could radically heel the canoe for pivot turns without shipping water over the gunwales, particularly in whitewater, while maintaing a vertical paddle placement. If you don't paddle like that, centrally shouldered tumblehome will be irrelevant to your paddling technique, even if it is available in a tandem canoe, in addition to detracting from seaworthiness.
I strongly recommend that you rent that Souris River Quetico 18.5 from an outfitter for your first trip. A long three-person canoe is a highly niche canoe and not a good long-term investment. Other than families with kids or long canoe racing teams (or motorized canoes), I'm not sure I've ever seen three adults paddling in one canoe on a wilderness trip. Personally, it would be anathema to me from every perspective—comfort, gear storage, trim, paddling coordination technique, safety, and autonomous freedom.
Moreover, you say you don't live in canoe country and are talking about driving thousands of miles for your initial canoe trip. Given those circumstances, I think it's highly unlikely that three adults will ever be able to organize their schedules, times, interests and motivations to undertake such long journeys to be cramped into one canoe . . . more than once. Hence, if you buy such an expensive beast rather than rent it, you may end up taking only one three-person trip in it your entire life. In such a case, you will end up owning a huge and very expensive canoe that most paddlers would find too awkward to solo and that may be hard to re-sell in non-canoe country.
Finally, I join all the others who have been suggesting that you would be more informatively served at this point by hands-on experience rather than further spec-scrolling. If you can beg, borrow, rent or otherwise test paddle some canoes—any canoes, with any amount of people in them—you can quickly "feel" what hull characteristics and specs are actually important to you. Warning: Your feelings and opinions will change over time if you pursue canoeing as a serious sport and as life circumstances change.