Has it been explained in Canon as to how gravity is kept while on board space faring vessals?

They have artificial gravity technology. What more is there to say ?

You mean using science jargon? Can't help with that but I do know that they have grav plates in the decks that they use to adjust and control the gravity inside the shipe and can raise or lower it as need be (examples of this would be found in Gunheads where the Cadians are sent to Galgotha to retrieve Yarricks Baneblade The Fortress of Arrogance)

How Grav Plating Works:

Due to the gracious nature of the most ancient and holy machine spirits of the Grav Plating, their harmonious chorus of will allows us to walk upon their magnificence instead of floating about the halls.

Do not belittle the most holy Grav Plating for allowing you to tread upon it. If you irritate their machine spirits they may ignore you and leave you floating about like driftwood in an ocean or, if you truly anger them, they might see fit to crush you into a gelatinous paste as if by an invisible heel of a holy Titan! Such is their wrath.

How Grav Plating Works:

Due to the gracious nature of the most ancient and holy machine spirits of the Grav Plating, their harmonious chorus of will allows us to walk upon their magnificence instead of floating about the halls.

Do not belittle the most holy Grav Plating for allowing you to tread upon it. If you irritate their machine spirits they may ignore you and leave you floating about like driftwood in an ocean or, if you truly anger them, they might see fit to crush you into a gelatinous paste as if by an invisible heel of a holy Titan! Such is their wrath.

Bravo!