* March WCS quoted at $30.80/bbl under WTI * March synthetic $0.50/bbl under WTI * Apportionment eases, Kearl start-up pushed back CALGARY, Alberta, Feb 4 Canadian heavy crude prices strengthened on Monday from last month's deeply discounted levels as pipeline constraints eased and Imperial Oil Ltd pushed back the start-up of its Kearl oil sands project. Western Canada Select heavy blend for March delivery last sold for $30.80 a barrel under benchmark West Texas Intermediate, compared with a Friday settlement of $30.50 a barrel under. Still, the spread is much narrower than last month, when WCS at times fetched more than $40 a barrel under. Apportionment levels on Enbridge Inc's pipeline network to the U.S. Midwest are below those set for last month, easing some of the pressure on heavy prices. The company put single-digit restrictions on Line 5, 4 and 67, and 21 percent apportionment on Line 6B. For January, the company imposed apportionment on some of its lines in Canada and the United States, but tacked on more restrictions in the middle of the month, which added pressure to already deeply discounted prices. Also, the start-up of Imperial's 110,000 barrel a day Kearl project in northern Alberta, first expected to begin commercial production at the end of 2012, is now targeted for the end of the first quarter, the company said last week. Full production is scheduled for the "next several months". Light synthetic crude for March delivery was quoted at 50 cents below WTI, a 35-cent deeper discount than on Friday. Synthetic prices have held their strength in the face of tight export pipeline capacity.