As a journeyman HVAC guy I would say it depends...
I lived in Alberta for over 20 years, (Calgary, Canmore) and the last thing we EVER had to worry about was too much humidity. One of the ways HRV's are ducted (and in my opinion the most energy efficient) is by drawing all the home air from bathrooms and closets. This eliminates all bathroom fans in the house. So instead of running a bathroom fan and exhausting that air outside and running an HRV beside that, only one appliance is running (the HRV) and you re-capture the heat from the air being exhausted from the bathroom. In this instance you have to run your HRV all year long because it is your main source of fresh air and exhaust.
Another way of ducting HRV's is drawing from other areas, high ceiling area's, hallways etc and it runs independently of your bathroom exhaust fan. In this case an HRV can be run only part time.
If you have A/C, this will take care of your humidity issues on it's own. The warm moist air will be draw into your central air system through the return air ducting and when it passes over the refrigeration coils of the A/C unit the moisture will condensate and run out of the condensate drain of your system. The dry cool air then gets distributed throughout your home. In this case, wingedfish is correct, the A/C will be fighting your HRV as the HRV continually brings in the warm air from outside.
You can get programmable switches for your bathroom exhaust fans that you can program to come on at certain intervals. This is what I've done in my place in an attempt to get rid of some humidity before it passes through my A/C system. I have my bath fan come on for 15 min every hour.
So i guess as a summary:
If you have A/C - I wouldn't run my HRV in the summer (assuming you have bath fans)
If you just have a furnace (no A/C) - I would run the HRV as long as the outside temp is cooler than the temp you want it inside your home.
Hope that helps