If you can rent an SUV with 4wd/awd for a reasonable price, it can help when heading out on powder days. You certainly don't "need" it, but I've passed people stopped on the hill to Nakiska spinning their tires.
If the snow's good, you'll want to be at the hill! Weekdays are better than weekends, but our hills don't get nearly as busy as other areas I've been (Whistler, Blue Mountain, Tremblant)
Others advice about just going where the road takes you is spot on. Minnewanka, Moraine Lake, Johnsons Canyon (if it's a warm day), are all worth seeing.
In Calgary, the Chicago Chophouse has fantastic Alberta beef, but it'll be $200 for the 3 of you. Famoso has good thin crust pizzas and a fun vibe. Many pubs/places on 17th ave SW (the Red Mile) if you just want to wander and go with what works. I like Fiore's for Italian. Alberta is known for it's meat so finding a restaurant with local beef, pork, etc. is going to be your best bet. Stay somewhere cheap in Calgary. Something near the airport is a little out of the way, but it's not a tough city to get around except at rush hours.
In Canmore, if you haven't booked a place, I like the Rocky Mountain Ski Lodge. It's a basic motel, but VERY well kept and probably better than most hotels I've stayed at for the price. For food, there's a Brazilian BBQ restaurant called Gaucho that's fantastic! If you're looking for something more fun, Grizzly Paw brewing has a brew-pub with good food and you can try any or all of their locally brewed 12 beers on tap. They have a 12 beer sample tray if you're into that.
In Banff, hotels are competitive, so check tripadvisor.ca for reviews before heading out. The Old Spaghetti Factory is fun and cheap, but don't expect fantastic food. Banff Ave. Brewing is another place I like to go for local good beer and food.
If you can stop in at the Bistro at Baker Creek Chalets (about 40 minutes West of Banff, 10 minutes East of Lake Louise). It's phenomenal. We had our wedding rehearsal dinner there last March, and stayed in one of the cabins on our wedding night. Most of my family said it was the best meal they've ever had. We did have the place to ourselves and a special menu, but I believe even a regular meal there should be FANTASTIC.
Johnsons Canyon also has some fun cabins near it for reasonable prices. Might be more fun than doing the "hotel on the strip" type Banff scene.
For the actual snowboarding: If you're looking to do something family friendly for the wife and kid, any of the local mountains will be fine. Might be best to wait and see who's getting the most snow. For tree boarding, Fernie is the best I've ever been to, but that's 3 hours from Calgary, 4-4.5 from Banff. Kicking Horse also has some amazing terrain, but it's 1.5 hours from Banff and there isn't much beginner terrain there.
Opinions on Lake Louise vs. Sunshine are like assholes. Everyone's got one. Locals fight over that argument like we fight over which hockey team is better (spoiler alert, I'm an NFL fan instead!). They both are beautiful resorts, they both have all the extreme terrain anyone visiting could ask for for a few days. I think Louise's treed terrain is more accessible and can be hit off the same lifts your wife and kid would be riding, so you could say "meet you at the bottom of this lift" and have your fun run while they stick to the groomers. I think everyone needs to see Sunshine on a bluebird day. It's an amazing scene looking around the whole valley and seeing nothing but mountains and runs.
During the week, Nakiska may be better for learning. It's a smaller hill (still 2400 ft of vert) and all the lifts are high speed except the bunny hill. You can go blast off laps and play in trees on the gold chair, while the wife and kid play on the silver chair. Nakiska always seems to get negative feedback on the forums, but I chose to Ski Patrol there because I like the hill, and I like how close it is to Calgary. If you're staying in Canmore or Banff, Sunshine or Louise will be closer, so it makes more sense to go to those two, unless Nakiska is getting the rare event of having more snow. It does happen.
P.S.: If you ever want to house swap, I need to spend more time in the sunny South! We just got back from a cruise and I want to move to St Maarten. The wife has a problem with me wanting to work on the cruise ships...