"Given the close integration between our economies, Canada's inclusion in TPP is the right decision and should be mutually beneficial. It will also give us the opportunity to correct the mistakes of NAFTA, especially on labor and the environmental standards," said Representative Sander Levin, the top Democrat on the House of Representatives Ways and Means Committee.
Harper said there were no conditions attached to Canada's entry to the TPP talks when asked if he would put supply management on the negotiating table.
"Canada has not agreed to any specific measures in terms of an eventual Trans-Pacific Partnership Agreement," he said.
"Canada aims, whenever it gets into a trade negotiations, to promote and to protect all of its interests across all the range of industries ... and Canada's record in terms of dealing with those particular issues in trade negotiations under our government has been very strong and that will continue to be our position," he said.
He said Canada would not seek to undo any progress already made by existing TPP partners and that the negotiations were in very preliminary stages. "As in any negotiations, nothing is agreed to until everything is agreed to by all parties."
Canada's accession to the TPP will take a period of time, he said, without giving details.
Therese Beaulieu, spokeswoman for the Dairy Farmers of Canada, a national lobby and promotional group for Canada's 12,965 dairy farms, said the group expected Harper to defend supply management. "Canada has been able to conclude a number of trade agreements before, and we've kept supply management. We have confidence that they can do it again."
Canada's opposition political parties oppose elimination of supply management but political analysts have said that even with opposition in farming areas, there is the potential for a political upside from urban voters if prices of milk and chicken fall.
Gerald Keddy, parliamentary secretary to the minister of international trade, reaffirmed on Tuesday that Canada did not give anything away to be part of the talks.
On Monday, Mexico also joined the TPP talks, while doubts remained over Japan's seven-month-old bid to join the negotiations. The other countries negotiating the trade pact are Australia, Brunei, Chile, Malaysia, New Zealand, Peru, Singapore, the United States and Vietnam.
Each member country must separately approve Canada's bid to join the talks. The government expects to have observer status at the next round of talks planned for July, but an agreement among the nine countries currently in the group is not expected for at least another year.
"Negotiations will likely extend well into 2013 before a deal is struck. It may even drift longer than that. But it is certainly do-able in the second half of 2013," said Jeffrey Schott, a trade scholar at the Peterson Institute for International Economics.
The Washington-based think tank on Tuesday released a study estimating the potential global income gains of a TPP pact at $295 billion, including $78 billion for the United States.
Schott said he expected Japan to come into the negotiations some time next year, and also expected South Korea to join before an initial deal is struck.
Japan's GDP is about $5.9 trillion and South Korea's is $1.1 trillion.