C172 and C182 both make fine planes for running surveillance. They're inexpensive (to buy and operate), reliable, inconspicuous, and have enough space and useful load to tack on specialized equipment. I used to own a 182 that was originally owned by the Washington State Police. While in WSP service, it was modified to have an automotive-style muffler for "stealth" surveillance.
According to him, the state much preferred to take cops and turn them into pilots, than to take pilots and turn them into cops. But anyone who wanted to go that route had to pay for their own flight time. (Commercial rating requires 250 hours, and I think they wanted at least a hundred hours "time in type." I don't think they required an ATP rating, but my recollection about that could be incorrect.)
The step up are the B1900s that CBP has which have additional sensor capabilities.