Both breeds tend towards being friendly with other dogs and non-aggressive, but of course to some extent it will depend on the individual dogs. The only thing I'd worry about is that boxers have a very rough play style (hence the name), but beagles are tough little dogs too--not very breakable lol.
One thing though, please please please do not get two puppies at the same time. Get one, then a year or two later get another. Two dogs is a LOT of work and two puppies is just way more than most people can handle. If they are very close in age and you aren't very very careful, they wll bond more closely with each other than with you and your wife, which can lead to big problems down the road. Even with two adults from rescue situations, I would not get them at the same time. Every dog has issues. From a breeder, pound or rescue, puppy or adult, chances are you will have some experience with some kind of problem: resource gaurding, nuisance barking, energy levels that are freakish and deserve close study by scientists, housetraining snags, seperation anxiety...I can gaurentee you that at some point you will have to deal with one or more of these problems, with any dog. Dealing with two new dogs and discovering their unique issues and qualities and personalities and doing the corrective work on whatever their problems are, well, I'd not sign myself up for that.
Let your wife get her beagle, earn big brownie points from her, then in a year or year and a half, start looking for your boxer.
Cressida and her best friends:
