I would wait with HRV/ERV for when you have ACH figures tested again. If you have enough ventilation through the envelope of the house (I don't know who in Canada sets the standards, in US ASHRAE sets up recommendations), the HRV might just cost you money (both initial outlay and ongoing electricity/maintenance costs) with only marginal increase of air quality.
Now if your house is really, really tight now (IIRC the target ideal figure to shot for in your climate is 0.2 ACH) you NEED to have some forced air exchange, especially if you use gas/propane inside.
The installation should not pose major headaches for a DIY type, for example look here: casaGURU: Install-It-Yourself HRV
I'm assuming the ACH test is done with a blower door - how much does the test cost in your neck of wood?