At a news conference in Vancouver Friday, Liberal Leader Michael Ignatieff said he would press to bring Khadr home if his party wins a federal election that could come as early as October.
"We find it extraordinary that the Conservative government would take this right up to the Supreme Court when we're talking about a Canadian citizen," Ignatieff said.
"Canadians have different views about Mr. Khadr's conduct. but that's not the issue. This man is a Canadian citizen. Guantanamo needs to be closed. Canadians think we should play our part in closing Guantanamo."
Toronto-born Khadr was captured by U.S. soldiers in Afghanistan in 2002, when he was 15, and has been held at the Guantanamo Bay detention centre for seven years. The U.S. accuses him of throwing a grenade that killed U.S. soldier Christopher Speer, but leaked documents have called into question the Pentagon's murder case against Khadr.
Khadr has been stuck in legal limbo since the swearing in of U.S. President Barack Obama, who vowed to close Guantanamo and repatriate all but its most serious prisoners.
But the Obama administration has yet to clarify its intentions for Khadr, and it now appears the controversial military tribunals at Guantanamo might still proceed.