A lot of internship postings also appear on Museum-L . A Canadian youth internship program that provides work experience for graduates. The Federal government has teamed with them to provide Public Sector Opportunities. As a result there are occasionally museum and heritage related positions. A great resource center which includes a Job Board, Internship Board, and Resume Board.
Users can freely post to any board using a form-based interface.
There are categories for Art History, Museums, and Non-Profit among others. Some of the programs include working in museums and heritage institutions. See also The National Graduate Registry for more information.