It's easier to enter England by sea than it is by air.
It's easier to go through immigration in England on a ship than it is by airplane.
この場合、次のような言い方ができますよ。
ーIt's easier to enter England by sea than it is by air.
「イギリスに入国するのに空より海の方が楽だ」
to enter England「イギリスに入国する」
ーIt's easier to go through immigration in England on a ship than it is by airplane.
「飛行機より船でイギリスの入国審査を受ける方が楽だ」
to go through immigration「入国審査を受ける」
ご参考まで！
カナダ 
