It would really be wonderful if you could say a few words at my wedding as the guest of honor. I know that it's possible you might not be able to attend in person, ...
so if I could trouble you to record a video message that we could play in such a case that would be greatly appreciated. Thank you so much in advance and I very much hope you will be able to come on the day.
随分短い挨拶（例えば2，3分ぐらい）の場合には "say a few words" 「多少言葉を言う」は決まり文句なんですが、もう少し長いスピーチを頼みたい場合には "short speech" 「短いスピーチ」を言っても良いです。その場合には"say a few words"の代わりに "make a short speech"を使って下さい。
下記には上司に書ける依頼依頼を書きました＝＞
「
It would really be wonderful if you could say a few words at my wedding as the guest of honor. I know that it's possible you might not be able to attend in person, so if I could trouble you to record a video message that we could play in such a case that would be greatly appreciated. Thank you so much in advance and I very much hope you will be able to come on the day.
」
随分丁寧に書きましたが、丁寧過ぎるではないと思います。
質問があればまた聞いてください。
ご参考になれば幸いです。
アメリカ合衆国 
