They both are accurate, both are flat shooters, both deliver excellent down range performance on game. The mag capacity is 3 on both rifles.
The 7MM uses bullets that have a little Higher BC. The 300WSM offers a hunting bullet selection above 175 grains. The 7 Mag does not.
The real distinction between the 2 cartridges are the rifle designs for each. The WSM is built on a short action, usually comes with a 23 or 24" bbl. and is a shorter, lighter rifle. It also headspaces off of the shoulder.
The 7MM Mag. is built on a magnum length action, usually has a 26" barrel, headspaces off of a belt above the head of the cartridge case. and is heavier and longer.
Both are great cartridges, both have excellent bullet selections to choose from.
Hope this helps.