Programs using the Sequoia Rust API are very likely to be source available, which satisfies the LGPL requirement.
Programs using the Sequoia Rust API which are not distributed do not need to do anything to comply with the LGPL.
Only proprietary Rust programs which are distributed to users need to really care. They can spend the modicum of effort to wrap the C-API.
If it were up to me, though, I'd choose MPLv2.
Programs using the Sequoia Rust API are very likely to be source available, which satisfies the LGPL requirement.
Programs using the Sequoia Rust API which are not distributed do not need to do anything to comply with the LGPL.
Only proprietary Rust programs which are distributed to users need to really care. They can spend the modicum of effort to wrap the C-API.
If it were up to me, though, I'd choose MPLv2.