Johnston was answering questions Tuesday at the University of Saskatchewan.
He says 150 years ago, the governor general may have had a theoretical right to veto a bill and did so from time to time.
But Johnston said that day is gone.
Just over 60 per cent of Prairie wheat growers and 51 per cent of barley growers voted in favour of maintaining the monopoly.
Fifty-five per cent of eligible wheat producers and 47 per cent of barley growers participated in the vote.
Johnston also said he's working to build relationships with members of all parties.
"I meet with the prime minister fairly regularly. I also make a point of meeting with the leaders of the other major parties, and I enjoy that very much," Johnston said.
He added he and his wife plan to host all the new MPs and their spouses for a dinner at Rideau Hall, the official residence of the governor general.
He says the evening will focus on the challenges and strains that public service can put on families and how to cope with some of those issues.