reply is long so short version is that i would accept the trade despite the concerns the above posters raise.
i have bruce as a keeper on my team and i like him a lot.
i agree that the keeper aspect might discourage this trade since bruce is probably the best keeper.
but ignore the keeper issue for a second. you're getting berkman, who was a better fantasy player last season, and cj wilson. espn ranks bruce as the 13th outfielder and berkman as the 19th outfielder. the difference between their auction values is three dollars ($21-$18). espn ranks cj wilson as the 17th starting pitcher ($15).
those two players are a significant return for your bruce. will bruce outperform berkman this year? bruce didn't last year, but i think it's very possible. but will bruce outperform berkman more than cj wilson will potentially outperform the player you drop? i doubt it.
going back to the keeper issue, i believe the highest priority at this stage of the season is to win the current season. perhaps the threshold issue to resolve is your chance of winning the league after this trade. if your team sucks (which it doesn't) and you significantly improve it at the cost of a special keeper (if bruce can be considered that), then you might decline the trade and preserve your keeper. but if your team is solid (which i believe it is) and you significantly improve it at the cost of a special keeper, then, at least for me, you make the deal.
bruce, prone to hot streaks, is hot right now with 3HR in 3 games. i believe your commissioner is overreacting to week 1 and you should take advantage.
edit: i misread the post. i thought commissioner already made offer. ask for the moon with bruce. he's hot right now and your commissioner might overvalue him.