Savage Model 24 in your favorite variant, and there were a number of them.
I would love to own a 12 gauge/.17 HMR over/under. But there are a number of shotgun/rifle combinations to suit your need. Assuming such gun is legal to hunt deer with in your state.
I would just use a different rifle for squirrel hunting than I would deer hunting. I am usually after one or the other, drastically different game generally calls for a different rifle.
I am a big fan of the .17 HMR for squirrels. In Georgia .22 Hornet is deer legal, and it is the smallest that is legal to use on deer. It would probably tear up a squirrel but if you aim for the head it would be accurate enough. It is a bit underpowered for deer in my opinion.