Depending on your capabilities as a shooter, I'd suggest either one of the hot .30's, or a .338WM.

A .308win mag, .30-06, .300WM, .300WSM would do you very well (preference in INCREASING order).

If you're a little more experienced, it's always nice to have an excuse to pick up a .338Win mag...although it's pretty heavy on recoil for a beginner. A .375H&H would do very well in what you've described too, but it kicks considerably harder, and I'm not ceratin your elk or bear get big enough to warrant the .375, however at the ranges you're asking about, you might NEED the energy!!

However, since you ask about rifle manufacturer too, it leads me to kind of assume you're not really experienced, and I'll say this, don't take a 300yrd shot. Until you've practiced shooting the rifle you'll be hunting with under hunting conditions at the range you're thinking about, it's just plain stupid to expect such great things. Most people don't even realize how far 300yrds is when they hear a rifle is "good for 300yrds on deer", until you've sat down and practiced it, you shouldn't be shooting that far.