bweber wrote:
I have traveled on a Viking River Tour. Your 18-135 will be fine for most things. You will not need anything longer than the 135, However, I would look for a wider lens for pictures in the city and town. There are very narrow streets, and many interesting buildings, doors etc. 18 MM on a crop sensor such as your Rebel is not wide enough for many good shots.
You can sometimes take multiple overlapping shots and stitch to panoramas later. Not so much where there are people.