Just about every bike on earth will handle 275 without any special considerations - the frames are plenty strong. It's really the wheels that suffer so the IMPORTANT aspect is to get them to put wheels on your bike that stand a chance. at least 32 spokes please! And you'll want them to retension the wheels after about 200 miles (not just true them).
Other than that, Giant is a good brand, they just don't market as much as Trek or Specialized.