I was there for the same reason at the end of June! There are always folks surf fishing on the beach (esp at dusk) and several fishing piers in the area. If you're interested in fly fishing though, I did speak with a couple guides pre-trip and also visited the folks at the Orvis store in MB. They all said the same thing: tough to target saltwater species during summer months. Inlet fishing in the flats is mostly done in the winter when the redfish come in. During the summer, they all chase warmwater species and there are tons of ponds all around MB that are stocked with bass, catfish, and carp.
I only got out to fish by myself briefly once (given the baseball schedule and didn't want to take time away from the kids' activities) and it was at a pond right by the ballpark. Had about 40 minutes and then got drenched by a late day storm walking back to the field. One way we did sneak in some fishing time and scratch the itch was a 1/2 day team outing on a head boat.
Good luck and enjoy it!