Asian shares held near eight-week highs on Thursday as investors bet on the likely size and scope of a bond-buying program the European Central Bank is poised to unveil later in the day in an attempt to revive the flagging euro zone economy.

The euro was quieter ahead of the ECB decision after the previous day's wide ranges, while the Canadian dollar stole the spotlight after plunging to a nearly six-year low following the Bank of Canada's surprise move to slash its overnight rate to help cushion the economy from recently plunging oil prices.

The loonie skidded almost 2 percent - its biggest one-day drop since November 2011 - to as far as $1.2420 per U.S. dollar, and last stood at C$1.2334, down about 0.1 percent on the day.

Broader market sentiment was mildly positive for riskier assets, supported by the aggressive actions by central banks seeking to fight deflation. Asian equities rose, U.S. yields were higher, and credit spreads were tighter.

MSCI's broadest index of Asia-Pacific shares outside Japan was up 0.2 percent, staying at nearly 8-week highs. Stock markets in Australia and Malaysia outperformed the region, while Japan's Nikkei stock average was flat.

The euro traded narrowly, between $1.1629 and $1.1589, moving away from an 11-year nadir of $1.14595 plumbed last week as the market trimmed short positions ahead of the ECB meeting.

Market analysts reckoned there was limited room for the euro to fall, given how high and for how long currency traders had been preparing for the ECB to expand its asset purchase program to include sovereign bonds.

A source told Reuters the ECB's Executive Board has proposed a quantitative easing (QE) program that would enable the bank to buy 50 billion euros ($58 billion) in bonds a month from March.

"The impact on the euro following such an announcement today is debatable given lofty market expectations, and a 'buy on rumor, sell on fact' reaction in the short term should not be ruled out, with a short squeeze likely unless something more significant than expected is announced," Barclays strategist Mitul Kotecha wrote in his daily note.

Kotecha however expects downward pressure on the euro to persist and for it to drop to $1.07 by end 2015.  

The dollar gained 0.3 percent against its Japanese counterpart to 118.27, still off Wednesday's gains after the Bank of Japan held policy steady.

The BOJ maintained its bullish inflation outlook for 2016 even as it cut its 2015 projections following falls in oil prices in recent months.

The Australian and New Zealand dollars suffered deep losses as the BOC's shock easing fueled speculation the Reserve Bank of Australia could soon follow suit.

The Aussie fetched $0.8083 , having shed more than 1 percent overnight. It was pulling closer to a six-year trough of $0.8033 set earlier in the month.

The kiwi tumbled to a 2-1/2 year low of $0.7545 .

Crude oil prices dipped on expectations that the ECB's decision to launch bond-buying stimulus could boost the dollar and put downward pressure on the commodity.

U.S. crude was down 34 cents at $47.44 a barrel.