* Canadian dollar weakens 0.4% against the greenback * Loonie touches weakest level since March 31 at 1.2623 * Canada"s trade surplus narrows in February to C$1 billion * Canadian bond yields trade mixed across a steeper curve By Fergal Smith TORONTO, April 7 (Reuters) - The Canadian dollar weakened to a one-week low against its U.S. counterpart on Wednesday as Canada deals with a variant-driven third wave of the coronavirus pandemic and domestic data showed the trade surplus narrowing in February. Canada"s trade surplus with the world narrowed in February to C$1 billion as a global shortage of semiconductor chips hit both imports and exports, Statistics Canada said. "A disruption in the global supply chain for chips significantly impacted the production of many products, notably motor vehicles as a number of North American plants had to stop production," said Ryan Brecht, a senior economist at Action Economics. Toronto, Canada"s largest school district, will cancel all in-person learning at elementary and secondary schools as of Wednesday, health authorities said. On Saturday, Canada"s most populous province of Ontario entered a limited lockdown. The Canadian dollar was trading 0.4% lower at 1.2609 to the greenback, or 79.31 U.S. cents, having touched its weakest intraday level since March 31 at 1.2623. Still, the loonie has climbed 1% since the start of the year, trailing only the Norwegian crown among G10 currencies. Better global and domestic economic outlooks have bolstered support for Canada"s commodity-linked currency. The International Monetary Fund on Tuesday raised its 2021 growth forecast for Canada by 1.4 percentage points to 5%, the biggest upgrade among G7 economies. The price of oil, one of Canada"s major exports, was lifted on Wednesday by prospects for stronger global economic growth. U.S. crude prices were up 0.7% at $59.76 a barrel, while Canadian government bond yields were mixed across a steeper curve. The 10-year rose nearly 1 basis point to 1.497%. Canada"s jobs report for March is due on Friday. (Reporting by Fergal Smith; editing by Jonathan Oatis)