I am in the market for a new bike, and the one that I am leaning towards is a Trek 1.2, but I have worries about my weight. I have ridden aluminum mountain bikes before, but am not sure if this bike will hold my 300 lbs. Any info?

300 lbs on aluminum isn't a problem at all. You might want to ask Trek about that particular bike, as it might have thinner tubing or something. But as a general rule, people bigger than you ride alu bikes every day. If anything, it's the wheels you should be worried about, and even then, get 'em re-tensioned, don't smack into curves, and enjoy the ride.

I recommend investing in a hand-built wheelset (or at least rear wheel). I've been commuting since 2003 (I was 205 lbs). Now, 260. (I know most people lose weight when they start a 20 mile daily commute not gain 55 pounds.) As my weight crept up over those years, the spoke breaking/truing issue on the rear wheel became a big problem across 3 different bikes (especially the inappropriate-for-a-daily-commuter-over-160-pounds stock wheelset on Trek Portland). I finally bought strongest possible wheelset from Peter White. Although I only have about 1500 miles on them, I feel confident that these wheels will outlive me without breaking a spoke or needed to be trued.

+300. When you buy the bike, get the shop to retention the wheels by hand as part of the purchase - if it's done by a mechanic who knows how to properly tension wheels (or at least can use a spoke tensiometer), they'll hold up as well as handbuilt wheels with the same components.