Given these points, it's unlikely that a high-quality, extra compressed ISO for "Call of Duty: Modern Warfare 3" for the Wii exists or would be feasible. However, if you're interested in similar gameplay on Wii, you might look into:

While "highly compressed" versions (like 700MB) are often advertised online, they frequently suffer from removed audio or corrupted textures. For the best quality, look for Wii Scrubber versions or Wii Scrubber Versions

for the Wii often leads to unreliable or unsafe sources. While the standard retail Wii disc size is roughly

Call Of Duty Modern Warfare 3 [ MULTI][ WII Scrubber][ PAL]. 7z : Free Download, Borrow, and Streaming : Internet Archive. Internet Archive Call of Duty MW3 Wii Installation Guide | PDF - Scribd

: When playing a "highly compressed" ISO on Dolphin, you can improve quality by increasing internal resolution (e.g., 3x resolution) to make the muddy Wii textures look sharper on modern screens. Critical Safety Warning