Can You Play with 360 Players in Call of Duty: Modern Warfare (Wii)? No — Separate Platforms

No. The Wii version of Call of Duty: Modern Warfare (Reflex Edition) cannot connect to Xbox 360 players.

Why

• Separate platforms: Wii and Xbox 360 have distinct online infrastructures (Nintendo Wi-Fi Connection vs. Xbox Live)
• Different game builds: Wii version is a separate port (by Treyarch) with reduced features, smaller maps, lower player counts
• No cross-play support: Not implemented in any CoD title of that era

Wii players can only match with other Wii players.