My weight went back to what it was before I went to Canada.
I returned to the weight I was before I went to Canada.
I lost 4kg while I was in Canada but I put it back on again when I went back home (to Japan).
「私はカナダに行く前と同じくらいに体重が元に戻りました。」＝ My weight went back to what it was before I went to Canada. / I returned to the weight I was before I went to Canada.
「カナダへ留学して4kg痩せたのですが、帰国して元に戻ったよ」＝ I lost 4kg while I was in Canada but I put it back on again when I went back home (to Japan).
ボキャブラリー
weight ＝ 体重
went back/returned ＝ 戻った
before I went to Canada ＝ カナダに行く前
lost ～kg ＝ ～kg痩せた
put it back on again ＝ 元（の体重）に戻った
when I went back home ＝ 帰国したら
イギリス 
