All renderers choose what to display and what not. Most however choose to not render historical objects with little to no visual appearance remaining, because OSM is mainly intended for today’s maps.
If you like, you can take a look at OpenHistoricalMap.org. It’s the go-to place for historical objects and natively renders them (within their time period). Note that it is much less populated compared to OSM and licensing is different, so you can’t just copy things from OSM to OHM.
If there are traces left of old canals (potentially non-continuous), then those can be mapped within OSM of course.
There is also a currently on-going project to map the Ludwig Canal (LDMK): Ludwig-Donau-Main-Kanal (Alter Kanal, Ludwigskanal). Perhaps it can help you too.