Shuffle off to Buffalo? That's what a lot of Canadian businesses are doing to beat Canada's expensive and strike-ridden postal service. Big and small Canadian mailers are shipping mail to border points and mailing the letters in the United States to cut costs.
This practice may accelerate with contract talks under way with Canada's inside postal workers, a group that in the past has been as unswerving as Britain's coal miners.
A first-class letter in Canada costs 32 cents; a first-class letter in the US costs 20 cents, which equals 26 Canadian cents. For a saving of 6 cents on a lot of mail, many companies are using courier firms to take their mail south.
A large-volume mailer opens a postbox in a a border city, say Buffalo for Toronto or Blaine, Wash., for Vancouver, British Columbia. At Windsor, Ont., and Detroit, the drive is five minutes, including customs clearance. A courier takes the mail down, posts it, and picks up the return mail.
''The large-volume (Canadian) mailers who have a large number of US consumers they want to reach just ship mail south,'' says a direct mail consultant. That of course is legal, as long as there is a return address in the US on the mail.
But other Canadian companies are breaking the law by mailing from the US back into Canada. Officials of the Canadian post office know about it but admit it's hard to catch anyone.
''There's not much we can do. It's pretty well impossible for us to police it ,'' said a spokesman for Canada Post, as the post office is officially called.
The post office is watching for mail sent from the US which has a Canadian return address. But often the return address is on the inside of the letters.
Postal officials estimate the practice costs at least half a million dollars a year in the Toronto region alone, according to a local postal official. The spokesman in Ottawa wouldn't hazard a guess on national cost.
Canadian businesses estimate that postal strikes in 1981 cost at least $30 billion (Canadian), according to a group called the Coalition Against Postal Abuse.
It points out that since 1965 ''there have been 59 work stoppages in the postal operation for a total of 2.5 million man-days lost to labor disputes.''
There may be more of that to come. The contract for the 23,000 inside postal workers expired Sept. 30.
The leader of the Canadian Union of Postal Workers, Jean-Claude Parrot, has been one of the most unyielding union leaders in the country. He is against reduced rates for bulk mailers, arguing that if it's cheaper for business it should be cheaper for everyone.
Parrot wants a reduced workweek, more job security, and more money. Postal clerks now get paid about $12.70 (Canadian) an hour, more than triple the minimum wage.
Because of the unreliability of the Postal Service, a lot of mail is sent by courier or electronically.
The Post Office carried 3.6 billion pieces of first-class mail in last year. That is down from the prestrike total of 3.8 billion in 1980 but up slightly from '82.
Canada Post receives a subsidy from Parliament of $300 million a year. Canada may have to raise postal rates next year, especially if there is a costly labor settlement. The US, on the other hand, has frozen postal rates until 1990.
If the first-class rate goes up or postal workers strike in the next few months, couriers shipping Canadian mail to border post offices may gain handsomely.