Probably more training of immigration officers would help. I get the feeling from immigration officers that they don't feel comfortable asking these questions. They don't really know how to judge the genuineness of a marriage in a lot of cases.
One simple fix that might eliminate the volume of the work is if the regulations or policy could be changed to where, if a marriage is clearly genuine, they not even engage in that kind of inquiry. For instance, just speaking arbitrarily, if the couple has been married for more than five years, if they've had children together, I don't know why it would even be necessary to embark on that.
It's a little off your topic, but I would go even further. In those situations where, for instance, there's a Canadian citizen sponsoring a spouse from overseas where the children are Canadian children by descent, if they want to reunite the family in Canada why even have a sponsorship of that non-Canadian spouse? I think that might free up some time. I don't have the stats on how many that would apply to, but it would certainly eliminate a lot of the angst for those families. The whole family can come to Canada as a right except the spouse who has to be sponsored.