Mulcair sent his letter to the premier's office Friday, as did Harper. Liberal Leader Justin Trudeau had previously responded.
If some of his fiscal commitments were vague, Mulcair seemed favourable to Couillard's requests and reiterated several times in the five-page letter that he would be a partner who would be open and ready to listen.
In response to Couillard's request for an increase in transfer funds for health care, to bring the amount to 25 per cent of the provinces' health care spending, Mulcair did not give precise numbers but said he would "work with the provinces and territories to ensure a better access to heath care as well as the long-term viability of the health-care sector."
Quebec's other big fiscal demand, of withdrawing the unilaterally imposed ceiling on the equalization program, was met with the same openness and scarcity of numbers.
According to the letter, which was put online Saturday morning, the NDP deplores the unilateral changes and is "ready to discuss the arrangements in the context of a larger discussion that will bring together all the partners of the federation and will take other federal transfers into account."
On the subject of international trade, Mulcair said his party favoured "an eventual trade agreement with Europe," which would "respect the federal government's obligations to compensate the dairy and cheese industry," he wrote, while promising to protect supply management when it comes to Trans-Pacific Partnership negotiations.
The tone of Mulcair's response to Couillard's "shopping list" of demands was comparable to that of Justin Trudeau: both stressing openness and a new era of collaboration between the federal government and the provinces.
Mulcair, however, reiterated his opposition to anti-terror Bill C-51, in contrast to his Liberal and Conservative rivals.
Both the opening and closing of his letter promised that if elected, he would be a partner and not an adversary, saying he wanted to "turn the page on a decade of indifference" in intergovernmental matters, because "the Canadian federation can and must work better."
Harper's letter, also published by Couillard on Saturday morning, stressed continuity, highlighting his government's contributions to the province and avoiding some of the more sensitive topics from Couillard's letter.
The letter promised to continue the "era of collaboration" that has presided since Couillard's election and committed to continue "to recognize the central role" of Quebec by practising "open federalism."
Harper did not commit to acting on Couillard's requests to increase health-care transfers to the provinces, remove the ceiling on equalization transfers, or standardize the calculation of dividends from the transport and distribution of electricity between Hydro-Quebec and Ontario's Hydro-One.
The letter stated that Quebec would receive $20.4 million in federal transfers in 2015-2016, an amount that would "continue to grow."
The Conservative leader also promised to continue working to oversee the spending power of the federal government as requested by Couillard and provide "reasonable compensation" to the province when it chooses not to participate in programs of "exclusively provincial jurisdiction."
While Harper agreed to Couillard's request regarding protecting supply management in the context of a trade agreement with Europe, and alluded to Quebec's requests for investments in shipbuilding, he did not address some requests such as restoring funding to Radio-Canada and abandoning the idea of tolls on the to-be-constructed Champlain Bridge.
Harper also took time to attack his Liberal and NDP rivals, whose proposals he said represent "direct encroachments on Quebec's jurisdiction."
Couillard's spokesman Harold Fortin said Couillard's government welcomed the responses from the three parties, saying "it shows a respect for the process led by Philippe Couillard."
Bloc Quebecois Leader Gilles Duceppe has said he also intends to respond to Couillard's letter.
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