You aren't going to find much common ground for the reason that they are two fundamentally opposed philosophies on how things ought to be done.
They no doubt agree on the ultimate end - a prosperous, healthy, happy country. But on all of the means to that end they are almost destined to have opposing prescriptions.
One common ground is anarchy. That's where extreme right and extreme left comingle.
The leftists see power as abusive and coercion as wrong, and people as generally good and able to organize themselves into syndicalist communes. The right sees government as overbearing and restricting freedom, as well as coddling citizens into whiney crybabies. They'd rather see everyone fend for themselves and the world run on free markets.
They can both agree that government is a problem and not a solution.
Not that that helps much.
I mean you can even take seemingly simple issues like crime. You'd think both sides could agree that there should be strong penalties for drunk driving. Not so. While the right might endorse stiff punishment, the left is unconvinced that prison serves much use in these cases and would be more in favour of a widened prevention program.
Child pornography - the left will worry about artistic rights and freedoms while the right will mount an all-out assault irrespective of such rights.
Veterans issues - I think this is an area where they might actually be in agreement. Both sides share respect for the sacrifices of our soldiers and want to see them taken care of by the society they fought to protect. They might differ on what that "care" should conssit of though.
Decentralization - in theory both sides should be for keeping power at the lowest levels possible, where it is close to the people who are effected by it. This would mean municipal and provincial empowerment. However, this has not actually happened yet so who knows.
