The right lens for architecture photography

The wider the angle and field of view. Is that what you are asking?

You are missing a wide angle lens from your lens collection.

Wide angle lenses are handy for interior shots.
But for interior, it is nice to have a bright lens.
Such as the Canon 16-35mm f2.8L

For low light shooting inside cathedrals and other dimly lit places, the Canon 50mm f1.8 lens is a very inexpensive solution ($80).

For external shots, Canon makes three Tilt Shift lenses. When you look at photos of the exterior of tall buildings, you will notice that the sides of the building seem to tilt inward . This distortion is caused by the fact that you are pointing the camera upward. A tilt shift lens will allow you to straighten the appearance of the building.
...But this can also be accomplished by using software, such as PhotoShop or PhotoShop Elements 4.

...............

Most people who have taken photos in Europe have said that their interior shots of cathedrals, churches, etc turned out poor due to the very dim lighting. The $80 50mm f1.8 lens will be your best chance for good results.

Just realize that you will likly be shooting at slow shutter speeds. Since most of these places will not let you bring in a tripod, you can take advantage of what is there. When hand holding the camera, lean against a wall, doorway, or pillar to steady yourself and the camera. When possible, set the camera on a steady surface (table, chair, etc). Just resting the camera on the back of a chair is helpful.

Good luck with your trip.

...
..
.

Sigma,Tamron, and Tokina lenses at focal length of 12-24mm are also available for much less expensive.

Take a look at a tilt shift lense. They are very expensive.