For details of specific canals and waterways, see Waterway Dimensions (pdf file), from the Canal & River Trust. Unfortunately, the "last updated" date is NOT shown in the text; however, checking "Properties" (or some similar term in your pdf viewer) may show you the date. On 9-Feb-2019, the one I downloaded was dated 31 July 2018.
Note that "headroom" as shown in the document is, as described in an email from the C&RT, "the height at which the width across the arch is equal to the 'gauge' of the canal in most cases. There are some cases where the definition is the highest point of the arch, but these are mostly for wide bridges." Water levels can also vary by several inches under normal conditions, or more dramatically during floods. This will also change the "headroom".
To double-check the above dimensions, we have John Russell's UK Inland Waterway Size Restrictions in English Units or his UK Inland Waterway Size Restrictions in Metric Units. These were last updated 17 Jan 2001, but since canal dimensions don't change much, they are still useful as a second source.
For visualizing narrow and wide canals on a map, see:
|Category||Tonnage (T)||Length (m)||Beam (m)||Depth (m)||Headroom (m)|
Armed with a large scale map of Europe showing the canals and their categories, one should be able to workout what routes are available. Be warned, as many French and Belgian canals may be only good for a depth of 1.8m not 2.2m. Usual problem of them not being dredged due to lack of money. (Thanks to Michael Clarke for supplying the above information.)
From "French Waterways", here's a map and tables for French Waterway Depths, Heights and Widths Here's a diagram, from french-waterways.com, showing how required "air draft" can vary with vessel width. The problem is actually more complex than shown there as the canal towpath can take up space on one side or the other under the bridge which has the effect of shifting any vessel toward a lower portion of the bridge arch.
I'm told that maps by Imray might fill the bill. Please email me if you agree/disagree. I am told (12/2006) that Imray's "Map of the Inland Waterways of France" does NOT give the width of the locks or the Category of the canals.
Euromapping, who used to produce the European Waterways Map and Directory, appears to have ceased trading. Waterways World magazine in April 2009 suggested that is was "the definitive map of Europe's rivers and canals". Too bad it's no longer available. The last edition may have been the 5th, in 2014. The map reportedly included information on both beam and channel depth.
Some information, and a book to buy, will be found at Michael Briant's Routes Between the English Channel and the Mediterranean.
See also PC-Navigo for (somewhat pricey) software.