Senior officials in the Obama administration said at a media briefing on Friday that Harper will be told privately the same thing he's been hearing elsewhere in public comments from U.S. decision-makers about the proposed TransCanada pipeline.
The message? There's a process underway in the U.S., the process is not politically directed, and it's not clear when it will end.
Harper is expected to raise the long-delayed pipeline when he meets President Barack Obama next week in Mexico at a North American leaders' gathering — and the answer's already in the can.
"What President Obama will do is explain to him where we are in the review ... and indicate that, of course, we'll let our Canadian friends know when we've arrived at a decision," one official said.
"Frankly, the message that he'll be delivering is quite similar to the one you've heard from us publicly."
The regulatory process has now entered a minimum 90-day phase during which Secretary of State John Kerry is welcoming input from different federal agencies. Then he'll make a recommendation to the president.
But it's not known how much longer than 90 days it might last — and the administration has repeatedly insisted that any political meddling will only slow things down, not speed them up.
Just a few days ago, Republicans in Congress were toying with the idea of attaching Keystone as a condition for their votes to extend the U.S. debt ceiling, but they backed away from the plan last week.
It was under similar deadline pressure from congressional Republicans that the Obama administration declared a reboot on the regulatory process before the 2012 election, setting back the timetable.
The Canadian government and the oil industry, for their part, hope for an answer before summer so that yet another construction season isn't wasted.
However, there's speculation in Washington that there might not be a decision until after the November mid-term congressional elections. In addition, even after a presidential decision, subsequent and ongoing lawsuits might continue to keep the project on hold.
The White House officials said Friday that they don't begrudge their Canadian counterparts for raising the issue — and they expect it to continue coming up in bilateral discussions.
"Look, we understand the interest of the Canadian government on this issue. They've been very clear with us, as they have been publicly, that they'd like to see this issue resolved," one said.
"We understand that. They are fully entitled to their opinion and their desire to see a conclusion of the process."
The regulatory process stems from an executive order, signed by George W. Bush, related to the rules for approval of energy infrastructure that crosses the border. White House officials said Friday that the final decision will be guided by two questions: Is the pipeline in the U.S. national interest, and will it significantly increase greenhouse-gas emissions?
The pipeline, whose southern leg is already operational, would carry oil from Alberta and the northern U.S. straight to refineries on the Gulf of Mexico, at a cheaper price than train transportation.
It would be just one of numerous pipelines in the U.S. but it has become the focus of an intense political debate as environmentalists decry Keystone XL as a project will unlock the full potential of Canada's oil sands.
A recent State Department report concluded that the oil sands will likely be developed at a similar pace — with or without Keystone — as long as oil prices don't get stuck below $75 a barrel and all pipeline projects get stalled.
Administration officials said that the Mexico summit will feature discussions about numerous other areas of joint interest and co-operation, including on the energy front on non-Keystone projects where the countries work together.
The three countries are also involved in negotiations for the Trans-Pacific Partnership, which could become the world's biggest-ever free trade deal.
However, the negotiations might be undermined by a steadfast refusal from congressional Democrats to grant the president fast-track authority. The U.S. Constitution gives Congress power over international trade deals and, without presidential fast track, each clause could be subsequently picked apart or rejected in a congressional vote, unravelling the process later.
It's not yet clear whether Harper and Obama will have a formal one-on-one meeting at the gathering in Toluca, the home town of Mexican President Enrique Pena Nieto.
Also on HuffPost