While the Canadian economy is struggling with the drag from weak oil prices, global events like Britain's vote to leave the European Union have increased its appeal.

"Foreign buyers view these assets as safe bets as they look to diversify their global real estate portfolios," said Ashi Mathur, head of North American real estate investment and corporate banking at BMO Capital Markets.

So-called Class A office buildings are high-quality properties in prominent locations that tend to draw the best tenants and command higher rents.

Class A sales in Canada in the first half of 2016 were worth $2.7 billion, compared with $415 million in the same period last year, with Vancouver and Toronto especially active, according to real estate services firm Colliers. Year-to-dates sales in 2016 have already surpassed full-year sales in 2014 and 2015.

Major deals involving foreign buyers over the past year include China's Anbang Insurance Group's [ANBANG.UL] purchase of Vancouver's Bentall Centre and Toronto's 70 York St. In another Vancouver deal, German billionaire Klaus-Michael Kuehne acquired the Royal Centre from Brookfield Canada Office Properties.

Chinese players have been particularly aggressive bidders, while European buyers have made more enquiries since the UK vote, real estate industry advisers said.

"Canada's weaker currency, combined with our lower volatility and lower geopolitical risk, makes us very appealing to certain foreign buyers today - notwithstanding where we are in the valuation cycle," said Jeffrey Dean, managing director at real estate-focused investment bank Trimaven Capital Advisors.

The Canadian dollar has strengthened against the U.S. dollar since the start of the year, but it has lost 19 percent since mid-2014, when a major decline in the price of oil began.

At the same time, the office vacancy rate in downtown Toronto fell to 4.9 percent in the second quarter, giving it the lowest downtown vacancy rate in North America, according to real estate firm CBRE.

Capitalization rates for Canadian Class A and AA properties are at their lowest level in at least a decade, especially in major urban centers, according to CBRE. Capitalization rates are calculated by dividing an asset's net operating income by its market price. A lower rate indicates stronger demand.

While sellers welcome the buoyant market, some wonder if the international interest will last.

"Is this influx of foreign capital temporary, an aberration, or is it part of a longer-term, sustainable trend?" said Paul Morassutti, an executive vice president at CBRE in Toronto.

"I would argue in a world that has so much uncertainty ... increasingly global investors are going to say Canada is a very good place to be."

(With additional reporting by Fergal Smith in Toronto; Editing by Jeffrey Hodgson and Jonathan Oatis)

By John Tilak