1. Lines of longitude run north-south, so you're right on that one.
2. Sailing along a line of LATITUDE will indeed get you to a little chunk of Algeria through the Strait of Gibraltar. Check a map.
3. Sailing in a straight line (full stop) is not possible, unless you're going very deep underwater to account for the curvature of the earth.
Sailing East from Michigan and Minnesota
Sailing West from New York, Pennsylvania, Ohio (barely) and Michigan (at Sault-Ste-Marie)
You can sail east from SC and GA to the Canary Islands of Spain. Also from all the states on the east coast goes a line to Mauritania and Senegal. From SC GA and FA goes a line to Cape Verde. From all the other states on the east coast, you can sail to the Gambia. From DE to SC you can travel to Guinea. From ME to NY and from GA and FA you can sail to Sierra Leone. From FA and GA, you can sail to Liberia. From NC to FA goes a line to Angola, Namibia and South Africa. From NC you can reach the west coast of Australia!!! It just goes between Brazil and South Africa. From AK you can sail to Chile, Norway and Denmark (Greenland).
And there are many many more!!! Watch the map for North-America via this link. You need to look very well because there are a lot of lines who start in Mexico or Canada.