The 2503 is dual 3 A w/o heat sink, 5 A peak. Adding a heat sink and /or fan would increase that capacity. This driver uses the MC33926 which has current limiting if you over heat it. Pololu test results delivered 5 A on both channels for 10 sec. before thermal protection started reducing the current. It delivered 4 A for 37 sec. before limiting. It did 3 A all day without limiting.
If you want lots of power, the 2502 can handle dual 25 A drive capability.
Here is a link to a table comparing all of their drivers Pololu - Comparing Products in 2 Categories
Bob Weber