How to obtain a logger inside a wagon?
Declare your own:
private static final org.slf4j.Logger _log = org.slf4j.LoggerFactory.getLogger(MercuryWagon.class);
How to select specific wagon implementation
Maven it picks the wagon implementation based on the repository protocol URL.
If you call your wagon "myw" and the URL is myw://superfast.com/my.jar, then if desired wagon has a role hint = myw, it will be selected for transport
Mercury wagon provider
Is described in detail here