In an enclosed area it's about 50/50, but I might give a slight edge to Gambit because he has more projectiles, which explode on impact, and he could get Cap off balance and away from his shield by doing so, but if Cap gets in close he has better H2h and Gambit has his staff fighting skills, so it's a good match. Enhanced athleticism is part of Gambit's mutation as well, so he can keep up in the agility department somewhat with Cap. He packs 52-55 grenades on him (if you count the 2 Jokers and the Game Suggestions Card that comes in the box). I remember reading a comic where Gambit charged some thug's teeth in his mouth and blew his head off (I think it was an Ultimate Xmen Book that I read online, I can't remember fully).
In an empty city street I'd take Gambit because he has more things that he can weaponize like debris, trash cans, soda cans, bottles, rocks, manhole covers, cars, his cards, buildings, etc. Gambit just has more offensive versatility.
Enclosed Area: 5/10 for both.
Empty Street: Gambit 7/10, possibly 8 if they are in a really rundown part of a city with a lot of trash and bricks and random objects laying around for him to weaponize. Fighting Gambit at a junkyard would completely suck.