Unfortunately, I don't think you've posted enough to actually provide a useful answer.
Depends on what you mean by 'Roku channel'.
- If a streaming provider, then that provider (not Roku) will determine video format standards
- if putting video on LAN/USB, and playing video directly on Roku, that isn't a 'channel' as commonly referred to. Further, some Roku devices are capable of 4K... Presuming modern 1080p, then widescreen 1080p, then 4K (2160 lines/rows, ie 2X 1080p, but called 4K for marketing reasons, breaking with decades of historical precedent, but I digress)
so ... (like many relatively new tech type things)... it depends (as there isn't a single, simple answer). sorry
As Aaron alludes to - H.264 standard TV aspect ratio/pixel count is different from what you listed. Not sure where you got that from???
Further, H.264 is a lowest common denominator (ie old), as the subsequent revision H.265 is a licensing mess, especially for free streaming platforms like YouTube, FaceBook, Twitch, etc (which therefore avoid H.265 source material, especially stream input). However, a true broadcast channel may well prefer H.265. The latest mass-market encoding format is AV1, which is intended to replace H.264 & H.265. However, in order to achieve its bandwidth savings (ie smaller recorded video file size) means FAR more computation up-front, and consumer grade real-time encoding hardware has JUST been released (ie.. bleeding edge).
So encoding format, depends on where and how you are sending the video? as a real-time Stream? or creating (Recording) local video file, and uploading/storing that someplace? There can easily be a difference in encoding recommendations between Recording and Streaming (depending on platform).
Best settings will more likely depend on what you Recording/Streaming hardware is capable of vs max possible settings your provider can accept.