wide & large
瀚 centers on vastness and expansiveness, like a wide ocean or a large open space. The given meaning 'wide & large' captures this sense of boundless extent.
瀚 combines 氵 (water) with 翰, which likely contributes the sound and the idea of something expansive or far-reaching. The exact historical development is uncertain.
The water radical 氵 beside 翰 suggests a huge ocean. Picture an endless sea stretching to the horizon: 瀚 is wide and large.
For カン, imagine a vast ocean that you can see all the way across: you can scan the wide water, and 'can' cues カン.
bulky; voluminous