Everyone may also benefit from more carefully reading the questions, implicit or otherwise.
The idea that comes from the OP is that he is looking for a "dream" rifle, made from a custom action and barrel, not a rebarreled and restocked Savage, however well some may shoot. Although he may not be certain about what disciplines he might eventually end up doing, he has some thoughts as to what he may be looking for.
The OP says "My current thinking is a right handed single shot, preferably with a left side port for feeding and ejection. It would sit in a quality front rest, riding a rear bag some of the time (but not always). I know Stiller's 2500X and Trident are popular down south, as is the Turbo. Does anyone in Canada carry these or import those?"
For what purpose are the types of actions to which the OP refers? They are single shot BR actions. For serious shooters, they are key components in many of the most commonly used custom BR rifles. These rifles typically use the quality rest system that the OP intends to shoot with.
Regarding the cost, it's not cheap. Components imported to Canada and gunsmithing costs might easily put it north of $3500 plus the wait. Of course, after hearing what a custom "dream" rifle would cost, the OP may well change his thinking to something less expensive and a little more available.
Regarding the barrel twist and chamber questions, it seems likely that he's read enough from online forums and elsewhere to be aware that some shooters are enthusiastic about faster twist barrels and that some chambers may be currently in fashion. Suffice it to say that it's very difficult to distinguish accuracy differences between two barrels of different twists when shooting long distances outdoors. Also suffice it to say that among the various match chamberings (there are literally dozens) there isn't one that stands out as being the most desirable. As always, ammo selection is more important.
While the OP says his range extends to 300 meters, it's worth noting that the actions to which he refers (with custom barrels) would be very effective in shooting long distances. They are not suitable, however, for PRS style shooting which generally favour a repeating rifle. For that purpose many shooters use Vudoo or RimX repeating rifles.