Would a XXL Dog Crate be a suitable cage for my Hollan Lop Rabbit?
This would be alright. Space is really important for your rabbit, so at least you are providing it with more, which is healthier in the long run. I would recommend you try to incorporate some upper levels or shelves, etc, into the cage so the rabbit has a second floor and a place to climb. For this you can use the same cube shelving units you would for a C&C cage, or just get some wood. You can attach these things with simple wire if they are light enough. As for cleaning, that all depends on the circumstances. Firstly, if your rabbit isn’t yet litter trained, I suggest you start on that. Having him go mostly in a litter box will make your life a lot easier; just change the litter box every day. As for the rest of the cage, it may be easier to avoid messy piecey bedding like hay, aspen, carefresh, as there is no barrier in a dog crate to keep them from toppling out. Many people are happy using carpet to line the cage, either paper or cardboard underneath to absorb urine. The carpet can