In 1846 I had a relative living in "Cat Fish Creek, Upper Canada". Is there any source I might access that would assist me in locating where this couple resided?

The Ontario Locator is a searchable directory of Ontario place names past & present.

When will the 1921 census be released?

The 1921 census is expected to be released to Library & Archives Canada on June 2, 2013. However there's no date set for when the LAC will allow public access to the census though it's presumed to be sometime later this year.

John Reid's "Anglo-Celtic Connections" provides excellent updates on the status of the 1921 census.