I suppose the answer to your question is that there is a "canon" order to the planet visits.
Oh, is there? Now I'm curious, which is [supposed] to be the canon order and where does this canon come from? I might wanna bear it in mind for my next replay some few years from now :-P. Unless I decide to go Dark Side and kill anything that breathes...
If you're asking me, I have no idea. I find the whole concept of canon
quite ludicrous. (Why have the option to play a female, if the character can only be male, for example, as in the canon?) This is a type of denormalization that diminishes the game, I think.
However, in the interests of conversation (I like the IP; I saw the first film at the cinema in 1977), I would suggest that Tattooine would be the first planet to visit. My reasoning is simple; the first protagonist, Luke Skywalker, who introduced us to the universe
, began the franchise on the desert planet, hence it would be the first place to visit for anyone who wanted to interactively re-live the first movie scenes & characters. This is no doubt why the Bioware put such an important back-story on this planet, assuming that —despite the ability to visit any of the four planets— most people will visit Tattooine fairly early in their play. (Think of the depth of the backstory for the Sand-people.)
Unless playing an evil character, most people would visit Korriban last, I would expect. (It is the most forbidding of the planets in the game, and there aren't any movies that contain it … though I haven't seen the last couple so that might not be correct now, but the point holds for all movies up to the release of this game.)
Whatever one might wish to explore in this creative venture (i.e., what piqued your interest; what film did you see first / had the most impact on you?) is where to follow after that.
Obviously, there is no reason to prescribe a journey; that completely defeats the purpose (and obviates all the effort invested by the developers) put to creating a non-linear adventure in the first place.