The Queen works well for Canada. If we become a republic then we are really just one step closer to being absorbed into the American polity in my opinion. I am sure there is nothing more tempting to a number of Yanks who still pine for the days of "manifest destiny" than for Canada to relinquish her Queeen and links with the past.
I personally think that the Queen promotes not only stability but also serves as a reminder that at one time Canadians were not democratic, that in fact not so very long ago we all lived in a society which although it followed the rule of law was unable to write them. The Crown serves as a constant reminder of our past particularly our own struggle to get responsible government. The Crown also represents a link with our more distant past that of the Angels, Saxons, Celts, and the creation of a very unique system of rights, laws,governance, language, world view something we can all be proud of.
I understand how some would be oppossed to the idea of monarchy. It is neither democratic or fair-of course neither is life. At its basis one assumes that God himself/ herself has chosen this individual to be sovreign, however, with this belief also comes great responsibilities for the sovreign, such as upholding and administering justice fairly, being merciful and protecting the state. The vows which the Queen promised to uphold are far more sacred than the mere words which are spoken upon presidential innaugurations. It is a covenant between monarch-state and people which can only be broken by death.
Someone wiser than me once said "that those who forget their history are condemmed to repeat it". I believe that the Crown promotes our history and helps keep us away from the slippery slope of historical ignorance and amnesia.