Hi Jerry,
You would push the Excel files to MSMQ for BizTalk just like you push any file to MSMQ (using System.Messaging or WCF). WCF-MSMQ is the way to go if you are using R2. The core transport is still MSMQ, you just use WCF to read and write to the queue. MSMQ does have a hard size limit. 4MB sounds about right. It sounds like you won’t come close to that limit, but if you do there are a couple of options. You could write code to chunk the files, send them to the queue, and then reassemble them on the other side. Alternatively, you could drop MSMQ altogether. The BizTalk message box itself behaves like a queue, so in many cases you don’t need MSMQ if you are using BizTalk. For example, you could set up a 2 node BizTalk group with a WCF http receive location on both servers and put them behind a load balancer. Now you have a highly available, load balanced channel into BizTalk. You can send a message into BizTalk via WCF, and it is automatically queued up in the message box.