While I agree that Martin will likely re-evaluate many of the reforms that Chretien has initiated lately, I doubt he'll reverse the Liberal position on gay marriage. Gay marriage is supported by a clear majority of Canadians, and cancelling support for this would cost the Liberals dearly. Once this reform has been initiated, it's hard to undo. As far as marijuana decriminalisation, its also a sticky issue. While we are risking pissing-off the Americans quite a bit, decriminalisation will save Canada BILLIONS of dollars in reduced demand on the courts' time and many fewer people being placed in prison. Marijuana related offenses represent a significant proportion of all cases before the courts and inmates in confinement.
Kyoto, on the other hand, is in serious danger. The reason for this has less to do any perceived conservatism on Martin's part than with the fact that Kyoto is a good idea in principal and a bad idea in execution. It doesn't do enough, and places the burden for reductions unevenly between the industrial and developing nations, as well as between industrial nations themselves. Australia, for instance, was allowed to increase its emissions by 8 over 1992 levels where Canada was required to reduce its emissions by 12% from 1992 levels. The reason we agreed to this was to show solidarity with the USA which was also agreeing to similar reductions. Obviously, since then the US has backed out of the treaty. And since the USA is no longer on bound, it would be quite contrary to Canada's interests to proceed with its commitment.
In other words, Kyoto needs to be renegotiated in light of the USA's decision to back out of the treaty.