Listening to the Conservatives and many Liberals you would think that Canada's international reputation raise and falls based on our willingness to waste billions of dollars on an Afghanistan mission that only serves to make it more likely that Canada will attacked by terrorists, home grown or otherwise. They could not be more wrong.
Canada's international reputation raises and falls according to our willingness to pass legislation that can serve as model for other countries, particularly other Western countries. SSM was a great case in point. No piece of domestic legislation has ever gotten so much international press, most of it positive, that I can remember. Moreover, not only did SSM debate receive plenty of press, the Canadian decision was important in many legal cases outside of Canada. If Canada were to legalize marijuana the amount for press this would receive would dwarf the coverage SSM debate received. Indeed, the amount for press Canada would receive in countries such as Mexico, Brazil and Columbia would quickly eclipse the amount Canada has received in those countries in the last 100 years.
As for what would happen domestically, of course Canadians will tell posters that they are far more concerned with other issues, of which they know next to nothing about, e.g., health care, but their willingness to talk about it at length will give lie to what they are saying. Actions speak louder than words. Needless to say, the press would be all over this issue.
Politically the Liberals would benefit in the same way that they benefited from the SSM debate. Namely, they would benefit from the Conservatives defending the same bad arguments day after day after day after day. (The country was evenly spilt when it came to SSM. However likely voters were not spilt. The Conservatives had the advantage. The older one was the more likley one was to oppose SSM and to vote. The Conservative arguments were terrible though and the issue received a tone of press between January 2005 and July 2005. The willingness of the Conservatives to trot out one bad argument after another hurt the Conservatives more than having the majority of likely voters oppose SSM hurt the Liberals. It was at the end of he SSM debate the Liberals were riding post sponsorship high in the polls and pundits were writing off Stephen Harper. The debate ended too soon for the Liberals though. The bill passed in July of 2005 and Fall session was dominated by Dingwall.)
BTW, the numbers for marijuana are far better than they ever where for SSM. Every poll in the last 3 years has put support for legalization in the low 50s and opposition in the high 30s.