both YEG and YYC have transit systems that work fairly well (the ctrain in YYC and bus system IMO is a bit better than ETS.) In terms of capacity, it is fairly easy to find space on most buses and subways, even during peak hours.
Keep in mind there are no turnstiles on either system (subway), so you insert a ticket into a machine that stamps the date on a transit ticket to pay the fare.
You can buy bus tickets in many places-most petrol stations have them.
This is the best option if parking is limited at the client site (which it has been for me.) but also depends in the location in which you choose to stay at and accessibility to transit.
As for YEG to YYC-the best way is by coach (if you drive, keep in mind any applicable mileage restrictions. Plan for $4/gallon petrol as well.)
As for driving in the winter-I admit I am terrible at it (I have only lived in YVR and have visited AB in the summertime.)
Public transport to and from the airport is more expensive than in the city. Expect 1/2 an hour for YYC to city center and 75 minutes from YEG to city center.