Hi Mike,
For the last few years I have used an HVLP gun for coating canvas, but prior to that I hand-rolled with Breathing Colour's Glamour II varnish and never had any problems with uneven coating on prints up to about A0 in size. The trick is to use a rather wet coat, work fast and then walk away from it without worrying about any remaining marks or unevenness; Glamour II has a relatively long drying time and levelling agents so that any marks should flatten out without further attention. A second coat if needed should take care of any visible variations in the finish.
I'm not sure I'd risk a large print with their Timeless varnish though, which is much quicker drying and without the levelling agents that make Glamour II so forgiving.
The only real downside I found with hand-rolling is that you need a large flat area for coating and that dust and hairs can get stuck in the print, which HVLP spraying generally avoids.
There are some useful tutorial videos on BC's site, and I believe they now also sell an 8" roller that they recommend for larger prints.
Cheers,
Malcolm