Dan has the right idea... Look up the towing information regarding the specific vehicle you are looking at. Be sure to take into considering the motor AND the rear end gearing.
A 2-place trailer, with sleds, will likely peak out at under 3000 lbs. A 4-place, with sleds, it likely to be closer to 5000-6000 depending on the starting weight of the trailer itself (you can generally use about 550lbs per sled as a working number to estimate weight).
Be mindful that you have to understand also that towing four sleds will mean you're also carrying two more adults in the vehicle AND all of their associated gear. This all has to be taken into account when figuring out GVWR, GTWR, and GCWR of your rig.