A collection started by employees had blossomed into an industry-wide show of solidarity, the Canadian Air Traffic Control Association told the BBC.
The partial government shutdown - now in its 24th day - has become the longest in US history.
It has affected 800,000 public workers and closed many government offices.
Air traffic controllers are among about 450,000 employees who are unable to suspend their work or take up another job, and so continue to work without pay.
By Sunday afternoon, more than 300 pizzas had been delivered to 49 control centres across the US, estimated Peter Duffy, the president of the Canadian Air Traffic Control Association.
"It was a true grassroots movement," Mr Duffy said, explaining that the initiative started with a few Canadian controllers wanting to show their colleagues across the border in Anchorage, Alaska, that they were thinking of them.
"They talk to those people daily on the phone... so they consider them co-workers and they said, hey, let's send them some pizza."
Since the first delivery last week, the gesture has spread nationwide, Mr Duffy said. "We have had one individual who donated C$500 (£377) and said 'find as many places as you can that need some pizza'."
He said Canadians would continue to support their American counterparts and join their calls for the shutdown to end as soon as possible.
Why is there a shutdown?
President Trump is refusing to approve a budget unless it includes funds for a wall along the Mexican border. Democrats have rejected his request for $5.7bn (£4.5bn).
About a quarter of the federal government is still out of operation until a spending plan is agreed.
On Friday, the affected federal workers - including prison guards, airport staff and FBI agents - missed their first salaries of the year.