what is the best way to receive and answer our emails and phone messages
1) Choose a Koodo US add-on that works for you and your needs. This is not the cheapest option, but it will be, by far, the most straightforward and convenient.
2) If your device is unlocked, and you plan on going to the US often, you should consider getting a US SIM card on a Pay as You Go plan. this requires visiting a brick and mortar store. Since I normally go down to the US for only about 1wk at a time, I've used T-Mobile's pay by the day plan with great success. Talk text and data for $3/day of use (Don't use it one day? then you don't pay).
Since T-mobile credit expires in 90 days and is hard to refill from canada unless you sign up for the online service (and even then there's no guarantee your card will remain active if you go a long time without using it) I've been considering getting a SIM from Roam Mobility as it is a bit more flexible.
Buy yourselves a Tracfone phone and buy a pay as you go card (from $19.95 for 60 minutes and certain phones triple this time). It will cost you much less in the long run. I've been using Tracfone for about 5 years now. I can call anywhere in the US and Canada (from the US) for 0.10 cents a minute, long distance or local. Plus the connection is super (except in the mountains). Excellent clear voice and you can also call International for the same low price. How cool is that? Nobody can beat this price. Plus when you buy a phone (about $20.) it's yours to keep. No fees whatsoever. Great company.