Lots of good info and ideas on the trailer/boat end of it here. I'll keep my comments to the locomotive side of your dilemma.
If you want this truck to be a daily driver, grocery getter, etc., and only plan to do maybe a few short towing trips a year, you'll be fine maxing out a 1/2 ton or a gas 3/4 ton (depending on what you're pulling).
On the other hand, if you want to do a significant number of long trips (think outside the province) and you have something else to use around town, you want a diesel. Some guys are fine with hitting the cruise control and revving their V8 gas engines to 5000 rpm on every little hill. I am not. With a strong diesel, you can chug along in a very relaxed way, pass tankers on a decent grade, and not worry about burning or blowing anything out. Newer trucks are quiet and comfortable, older ones are less so but tend to be extremely reliable. What you end up choosing depends on what's important to you.
To me, it's all about the engine. That's what's going to get you there at the end of the day. Sure, my Dodge is relatively loud, rough, and at risk for some steering issues. I don't really care. It's got the greatest engine ever put in a pickup and it will probably be going 25 years from now. You'll find advocates of the Duramax and Powerstroke motors all over the place, but you haven't towed till you've towed with a Cummins.
Taking this rig 1600 km to Prince Rupert and back almost every summer for the last 5 years has cemented some of my opinions on the subject.