You need to take a final gravity to get an accurate answer.
You had 3 gallons with an OG of 1.070. Two cans of concentrate is roughly 0.2 gallons, so batch size is now 3.2 gallons. Ignoring the sugar in the concentrate for a second, the OG in the larger batch would be 1.066
1.070 * 3 / 3.2 = 1.066
One can of concentrate typically adds 17 points to a one gallon batch. Two cans would add 34 points in a gallon batch. In a 3.2 gallon batch two cans would add approx. 11 points.
34 / 3.2 = 11
Taking the concentrate addition into account, your adjusted OG is 1.077
1.066 (or 66) + 11 points = 1.077
Once you know your final gravity (FG), you can subtract it from your OG to calculate your ABV. If it ferments to 1.000, you'll have approx. 10% ABV. 0.993 would be about 11% and 1.008 would be around 9%
i think its 1 lb of shugar is roughly = to 10 points, but if thats wrong im sure someone will correct me. its your FG which is now irrelevant, the only point of checking gravity at this point is to see when its done (around 0.995)
starting with the min ABV just find how many grams of sugar were in the concentrate and from that find how many grams of sugar you added to the cider. convert grams to lbs, convert lbs to gravity points and there you go.
Your FG is relevant. You need to know how far it fermented. One lb of sugar adds 45 points (1.045) in a one gallon batch. In a 3 gallon batch it would add 15 points (45 / 3 = 15). Nutritional labels usually express sugars in grams. Converting to lbs isn't necessary. It's easier to do the math in grams. 10 grams of sugar will raise one gallon by 1 point. For example, if your two cans of apple juice concentrate contain 340 grams of sugar, you just divide by ten and get 34 points in one gallon. Simple. When doing calcs this way, always expess gravity to three decimal places to avoid confusion. 10 grams of sugar per gallon raises the gravity by 1.001, not 1.01.