Establishing a balanced, rhythmical walk and trot is essential for the development of a good quality canter. If you do not have a good connection established in walk and trot, you will struggle with it in canter unless the horse has a naturally very good quality canter and not so good walk/trot.
Have a think about it. If you go into canter from a hollow, strung out trot, the transition will be hollow and strung out, and the canter will be hollow and strung out.
If you enter the canter from a well balanced, soft and engaged trot, the transition will be uphill, light and balanced, and the canter will also be uphill, light and balanced.
Developing a good quality trot is so important for a good quality canter! So no, I don't think you can ever do too much trot work. Walk yes, you can destroy a walk doing too much, but not trot.
Of course, as someone said above, if you are just trotting around, not changing or improving anything about the horse's way of going, allowing it to work strung out, stiff and on the forehand, you're not doing anyone any favours and of course the canter will be of bad quality.