** Canadian gas retailer and convenient store operator’s shares fall 8.3 pct to C$59.13 on margin pressure
** On pace for worst day since Dec. 1, 2008; top decliner on TSX consumer staples sector
** Q3 gross margins in fuel business in co’s biggest market, U.S., decline 14.6 pct due to higher crude prices
** Revenue from the business in region jumps 51.3 pct on higher selling prices
** Total revenue climbs 38 pct; net income surges 62 pct
** Stock down 3.6 pct this year (Reporting by Medha Singh in Bengaluru)