您可以按照此Docs通过检查设备是否安装了HMS Core APK来检测华为设备。

// Create an HmsApiAvailability instance
HmsApiAvailability client = new HmsApiAvailability();

// 0: HMS Core (APK) is available.
// 1: No HMS Core (APK) is found on device.
// 2: HMS Core (APK) installed is out of date.
// 3: HMS Core (APK) installed on the device is unavailable.
// 9: HMS Core (APK) installed on the device is not the official version.
// 21: The device is too old to support HMS Core (APK).
int status = await client.isHMSAvailable();

**更新：**device_info插件现已停用。

使用https://pub.dev/packages/device_info_plus，它提供了类似的功能。
您可以找设备制造商来检测华为设备

DeviceInfoPlugin deviceInfo = DeviceInfoPlugin();
AndroidDeviceInfo androidInfo = await deviceInfo.androidInfo;
print('Running on ${androidInfo.manufacturer}');

使用的插件-https://pub.dev/packages/device_info

或者

您可以检查设备中GooglePlayServices的可用性

GooglePlayServicesAvailability availability = await GoogleApiAvailability.instance.checkGooglePlayServicesAvailability();

需要插件-https://pub.dev/packages/google_api_availability

**注意：**如果使用GooglePlayServices检查，还需要添加平台检查，因为iOS设备返回false。

判断设备中HMS是否可用的方法如下：
HuaweiApiAvailability.getInstance（）.isHuaweiMobileServicesAvailable（context）
检查HMS是否可用。

public class HmsGmsUtil {
    private static final String TAG = "HmsGmsUtil";

    /**
     * Whether the HMS service on the device is available.
     *
     * @param context android context
     * @return true:HMS service is available; false:HMS service is not available;
     */
    public static boolean isHmsAvailable(Context context) {
        boolean isAvailable = false;
        if (null != context) {
            int result = HuaweiApiAvailability.getInstance().isHuaweiMobileServicesAvailable(context);
            isAvailable = (com.huawei.hms.api.ConnectionResult.SUCCESS == result);
        }
        Log.i(TAG, "isHmsAvailable: " + isAvailable);
        return isAvailable;
    }
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    mHmsSignBtn = findViewById(R.id.hms_sign_btn);
    mHmsSignBtn.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            signInByHms();
        }   

    mGmsSignBtn = findViewById(R.id.gms_sign_btn);
    mGmsSignBtn.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            signInByGms();
        }
    });

    boolean isHmsAvailable = HmsGmsUtil.isHmsAvailable(this);

    Log.i(TAG, "isHmsAvailable: " + isHmsAvailable + ", isGmsAvailable: " + isGmsAvailable);

    if (isHmsAvailable && !isGmsAvailable) {
        // Only hms, Sign In by huawei account.
        mHmsSignBtn.setVisibility(View.VISIBLE);
    } else if (!isHmsAvailable && isGmsAvailable) {
        // Only gms, Sign In by google account.
        mGmsSignBtn.setVisibility(View.VISIBLE);
    } else if (isHmsAvailable && isGmsAvailable) {
        // both hsm and hms, decide by developer.
        mGmsSignBtn.setVisibility(View.VISIBLE);
        mHmsSignBtn.setVisibility(View.VISIBLE);
    } else if (!isHmsAvailable && !isGmsAvailable) {
        // neither hms and gms, decide by developer.
        mHmsSignBtn.setVisibility(View.VISIBLE);
    }
}