I know this answer is late and such but i wanted to share this anyway. This worked for me:
vnd.youtube://user/channel/channel_id
This opens the channel directly in the youtube app. Without asking the user.
Update
Didn't include any code because i was using React Native, and maybe people is looking for native code. Anyway here you go:
Linking
.openURL( 'vnd.youtube://user/channel/' + channel_id )
.catch( ... )
But, i think in native code it should be something like this:
Intent appIntent = new Intent(Intent.ACTION_VIEW, Uri.parse("vnd.youtube://user/channel/" + channel_id));
try {
context.startActivity(appIntent);
} catch (ActivityNotFoundException ex) { ... }
I'm not too familiarized with native code so it may be wrong, but should work like a guide.