Last time I bought an a/c, the companies quoted in tons. Now they quote in BTU's. What is the approximate conversion between BTU's and tons?
My apartment is 40 ft long by 26 ft wide (1040 sq ft) with 8 ft ceilings. The windows face north and south. East and west are just the walls of the adjacent units. I'm on the second floor, so my unit is virtually insulated by all the surrounding units. And I face a lake, so the breeze is wonderful. What size A/C should I get?

1 ton = 12,000 BTU for cooling.

Although there are other factors to consider, for a single level, you can roughly approximate about 1.5 tons per 1,000 sq.ft. Insulation,window,ambient heat load play a deciding factor. You will need more BTU/ sq.ft. in AZ vs AK.