Source of Rains is the worst part of the stage. It's not hard or anything, just really annoying and boring and stupid and what the fuck was ZUN thinking.
Anyway, there are always gaps in VoWG. The trick is to play it a million times so that you recognize every pattern that appears in it, read these patterns while they are bunched up near Kanako, and react appropriately to move into the gaps. These gaps are sometimes very small or very short lived.
For example, 4:26 in
this video is an example of a very small gap (it's still larger than trying to micrododge between the individual cards in a given wall). 4:38 is an example of a very short lived gap - the space I dash through is only open for a split second. A similar pattern occurs at 4:48.
Despite these gaps looking very difficult to get into, they really aren't once you can see them coming and have some practice with them. Again, that just takes practicing the card a million times, so that you can familiarize yourself with the finite number of patterns the overlapping card walls can make.