I doubt spray oil would have any effect on canker. Dormant oil spray on roses is sometimes recommended for mite control.

Unfortunately we have little or no research on rose canker control and fungicides aren't labelled for it. There are various fungi involved. Dormant spray of lime sulfur helps control some of them if applied in late fall and again in late winter. It may be that modern fungicides would be more effective, but nobody knows. Lime sulfur is hazardous and disagreeable to handle.

It seems logical that a dormant-strength anti-transpirant applied over a broad-spectrum fungicide or even alone would keep fungi from entering wounds in the bark. I do this some years but have no way to measure the effectiveness.

Mich, what is the name of the product you use?

Wilt Pruf, maybe with Daconil. Wilt Pruf alone is considered organic.