红孩儿 thinks 唐僧 tastes nice. He wants to eat him, but 孙悟空 is onto him. Leaving aside the important question of how he knows 唐僧的味道好, what does this 硬 mean?
看来，硬捉是不行的，不如换个方法！
I'd like to translate: 硬捉 directly grab him, just grab him，but I don't find these meanings for 硬。
硬：hard, strong, tough, firm, obstinate.
Is there another Chinese word which could replace 硬 here?
硬 here connotes forcefully, without any tactics and etc.
硬捉 means to capture/seize/catch merely by force, without any tactics.
So,
看来，硬捉是不行的，不如换个方法！
Looks like, the way of capturing forcefully (without any tactics) wouldn't work, so we might as well change/turn to another way.
The synonym of 硬 in this context can be 强.
Generally, 软 mean soft and 硬 means hard, also there are other extended meanings, like the idiom, 吃软不吃硬 literally meaning: prefer eating soft (tender method/attitude) rather than hard (tough method/attitude), meaning: (one could only) succumb to tender attitude but not tough attitude. 硬捉是不行的: It is infeasible to catch him toughly, or, It is infeasible to catch him directly.
硬 in here means hard way , so 硬捉 means hard way to catch
