Personally, unless there's been a lot written about a character from canon fiction (for example, the majority of the "Notable Pilot" blurbs in the original
TRO: 3025 would be perfect for this), I think taking a character that's had a paragraph written up and running from there is a great idea. It's how I usually begin to flesh out my own characters: start with a paragraph to two that says something about the character's motivations, skills, background, appearance, and personality and then build from there.
Now, for taking a canon "scene" and putting folks into those characters...well, the more wiggle room you have for the players (as opposed to their PCs) to act out of established canon, the better. It's
very easy to get drawn down into an argument of, "VSD would
never do that!" "Yeah, he would; see, he's got this Big, Dark Secret that's been gnawing at his soul." "Why didn't Stackpole ever write about that, then, hmmm?" "Because I just made it up." "Oho, so you're
not playing Victor, then?" "Yes, I am; see this character sheet right here?" "That doesn't mean you're playing
him; you're not playing him true to type." Etc...
Now, if you wanted to do a scene from canon to go over game mechanics, I'd rather pick something from one of the various short fiction pieces out there. They tend to involve characters that are less well-known and have less universe-changing effects. Stuff like
May Black Cats Cross Your Path from the (2nd ed?) Mechwarrior game book would be better. It involved a unit that I'd never heard of before or since and didn't go into deep, soul-searching motivations. Instead, it presented a good action scene involving an infantry unit taking on 'Mechs in an urban setting.
Anyway, what I'm saying is that, while you need to give your characters structure, you also need to not straitjacket them into specific roles and responses. It's a fine balance, and there have been
much better articles written on it than I could ever do. If you want a good resource for GMing advice (a lot of it is d20-specific, but there's a lot that's general advice, too), this guy has a lot to say, most of it good advice:
http://www.thealexandrian.net/creations/creations.htmlHope it helps!